Structure and method for interconnection

ABSTRACT

Various self-aligned interconnect structures are disclosed herein. An exemplary interconnect structure includes a first dielectric layer disposed over a substrate; a first conductive feature disposed in the first dielectric layer; an etch stop layer disposed over a top surface of the first dielectric layer and a top surface of the first conductive feature; a second dielectric layer disposed over the first dielectric layer; and a second conductive feature disposed in the second dielectric layer. The top surface of the first conductive feature is lower than the top surface of the first dielectric layer. The etch stop layer includes a portion that extends between the top surface of the first conductive feature and the top surface of the first dielectric layer, on which the second conductive feature may or may not be disposed. In some implementations, the second conductive feature may be a via feature.

This application is a continuation application of U.S. patentapplication Ser. No. 15/634,778, filed Jun. 27, 2017, now U.S. Pat. No.10,290,536, which is a divisional application of U.S. patent applicationSer. No. 14/829,851, filed Aug. 19, 2015, now U.S. Pat. No. 9,698,100,the entire disclosures of which are incorporated herein by reference intheir entirety.

BACKGROUND

In semiconductor technology, an integrated circuit pattern can bedefined on a substrate using a photolithography process. Dual damasceneprocesses are utilized to form multilayer copper interconnectionsincluding vertical interconnection vias/contacts and horizontalinterconnection metal lines. During a dual damascene process, a plugfilling material is employed to fill in the vias (or contacts) and thematerial is then polished back. However, the vias (or contacts) aredefined by a different lithography process and may cause misalignmentsbetween the underlying metal lines and the vias. Especially, when thesemiconductor technologies move forward to advanced technology nodeswith smaller feature sizes, such as 20 nm, 16 nm or less, themisalignments have less tolerance and may cause short, opening or otherissues.

Therefore, the present disclosure provides an interconnection structureand a method making the same to address the above issues.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a flowchart of one embodiment of a method to form anintegrated circuit (IC) structure, in accordance with some embodiments.

FIGS. 2, 3, 4, 5, 6, 7, 8, 9 and 10 illustrate sectional views of anexemplary integrated circuit structure during various fabricationstages, made by the method of FIG. 1, constructed in accordance withsome embodiments.

FIG. 11 illustrates a top view of the integrated circuit structure, inportion, of FIG. 4 in accordance with some embodiments.

FIG. 12 illustrates a sectional view of an integrated circuit structureby the method of FIG. 1 in accordance with some embodiments.

FIG. 13 illustrates a sectional view of an integrated circuit structurein accordance with some embodiments.

FIG. 14 illustrates a sectional view of an integrated circuit structureby the method of FIG. 1 in accordance with some embodiments.

FIG. 15 illustrates a sectional view of an integrated circuit structurein accordance with some embodiments.

FIG. 16 illustrates a sectional view of an integrated circuit structureby the method of FIG. 1 in accordance with some embodiments.

FIG. 17 illustrates a sectional view of an integrated circuit structurein accordance with some embodiments.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the formation of a first feature over or on a second featurein the description that follows may include embodiments in which thefirst and second features are formed in direct contact, and may alsoinclude embodiments in which additional features may be formedinterposing the first and second features, such that the first andsecond features may not be in direct contact.

FIG. 1 is a flowchart of a method 100 to form an integrated circuitaccording to one or more embodiments of the present invention. FIGS. 2through 10 illustrate sectional views of an exemplary integrated circuit200 during various fabrication stages of the method 100. With referenceto FIGS. 1 through 10 and other figures, the method 100 and theexemplary integrated circuit (IC) structure 200 are described below.

The method begins at 102 by providing or receiving a substrate 210 asillustrated in FIG. 2. In some embodiments, the substrate 210 includessilicon. Alternatively, the substrate 210 may include other elementarysemiconductor such as germanium in accordance with some embodiments. Insome embodiments, the substrate 210 additionally or alternativelyincludes a compound semiconductor such as silicon carbide, galliumarsenic, indium arsenide, and indium phosphide. In some embodiments, thesubstrate 210 includes an alloy semiconductor such as silicon germanium,silicon germanium carbide, gallium arsenic phosphide, and gallium indiumphosphide.

The substrate 210 may include an epitaxial layer formed on the topsurface, such as an epitaxial semiconductor layer overlying a bulksemiconductor wafer. In some embodiments, the substrate 210 includes asemiconductor-on-insulator (SOI) structure. For example, the substratemay include a buried oxide (BOX) layer formed by a process such asseparation by implanted oxygen (SIMOX). IN various embodiments, thesubstrate 210 includes various p-type doped regions and/or n-type dopedregions, such as p-type wells, n-type wells, p-type source/drainfeatures and/or n-type source/drain features, formed by a process suchas ion implantation and/or diffusion. The substrate 210 may includeother functional features such as a resistor, a capacitor, diode,transistors, such as field effect transistors (FETs). The substrate 210may include lateral isolation features configured to separate variousdevices formed on the substrate 210. The substrate 210 may furtherinclude a portion of a multilayer interconnection (MLI) structure. Themultilayer interconnection structure includes metal lines in a pluralityof metal layers. The metal lines in different metal layers may beconnected through vertical conductive features, which are referred to asvia features. The multilayer interconnection structure further includescontacts configured to connect metal lines to gate electrodes and/ordoped features on the substrate 210. The multilayer interconnectionstructure is designed to couple various devices features (such asvarious p-type and n-type doped regions, gate electrodes and/or passivedevices) to form a functional circuit.

Still referring to FIGS. 1 and 2, the method 100 includes an operation104 by forming one (or more) underlying conductive feature 215 on thesubstrate 210. In some embodiments, the underlying conductive feature215 is a doped region, such as a source/drain feature. In someembodiments, the underlying conductive feature 215 is a gate electrode,a capacitor or resist. In some embodiments, the underlying conductivefeature 215 is a metal feature, such as a metal line, a via feature or acontact feature. In some embodiments, the underlying conductive feature215 includes both a metal line and a via feature.

In the present embodiments for description), the underlying conductivefeature 215 is a metal line in one metal layer of the MLI structure. Infurtherance of the embodiment, the underlying conductive feature 215 isformed in a first dielectric material layer 220.

In some embodiments, the metal line 215 is formed by a damasceneprocess, which is further described below. The first dielectric materiallayer 220 is formed on the substrate 210. Alternatively, an etch stoplayer 225 is formed on the substrate 210 and the first dielectricmaterial layer 220 is formed on the etch stop layer 225. In someembodiments, the first dielectric material layer 220 includes adielectric material such as silicon oxide, silicon nitride, a lowdielectric constant (low k) material, or a combination thereof. The lowk material may include fluorinated silica glass (FSG), carbon dopedsilicon oxide, Black Diamond® (Applied Materials of Santa Clara,Calif.), Xerogel, Aerogel, amorphous fluorinated carbon, Parylene,bis-benzocyclobutenes (BCB), SILK (Dow Chemical, Midland, Mich.),polyimide, porous polymer and/or other suitable materials as examples. Aprocess of forming the material layer 220 may utilize chemical vapordeposition (CVD), a spin-on coating or other suitable depositiontechnology. The etch stop layer 225 includes a material different fromthe first dielectric material layer 220 designed to provide etchselectivity such that a subsequent etching process is able tosubstantially etch the first dielectric material layer 220 and stops onthe etch stop layer 225. For example, the etch stop layer 225 includessilicon nitride, silicon oxide, silicon oxynitride, silicon carbide orother suitable material that functions to stop the etching of thesubsequent etching process. The etch stop layer 225 may be formed by CVDor other suitable technology. After the deposition of (the etch stoplayer 225 and) the first dielectric material layer 220, the firstdielectric material layer 220 may be further planarized by a technique,such as chemical mechanical polishing (CMP).

Thereafter, the first dielectric material layer 220 is patterned to formone or more trench. The trench may be aligned to expose lower conductivefeatures in the substrate 210 such as metal features in a lower metallayer or alternatively doped regions disposed in the semiconductormaterial of the substrate 210. In some embodiments, an operation to formthe trench utilizes a lithography patterning and etching processes knowin the art or by a new technique to be developed in the future. Forexample, a patterned resist layer is formed on the first dielectricmaterial layer 220 by a lithography process that includes resistcoating, exposure and developing. The patterned resist layer includes anopening that defines a region for the trench. An etching process isfurther applied to the first dielectric material layer 220 through theopening of the patterned resist layer, using the patterned resist layeras an etch mask. After the formation of the trench, the patterned resistlayer is removed by wet stripping or plasma ashing. Alternatively, ahard mask may be used such that trench pattern is transferred from thepatterned resist layer to the hard mask by a first etch and thentransferred to the first dielectric material layer by a second etch.

A conductive material is then filled in the trench to form theunderlying conductive feature 215. In various embodiments, theconductive material includes copper, aluminum, cobalt, or tungsten. Insome other embodiments, the conductive material may include titanium,polysilicon, metal silicide, metal alloy, or combinations thereof. Inthe present embodiment, the underlying conductive feature 215 includescopper and has multiple films. In furtherance of the embodiment, theunderlying conductive feature 215 includes a barrier layer lining thetrench and copper filled in the trench. In one example, the underlyingconductive feature 215 is formed by a procedure that includes depositinga barrier layer on sidewalls of the trench; forming a copper seed layerby sputtering; and filling the bulk copper in the trench by plating. Thebarrier layer may include titanium, titanium nitride, tantalum, tantalumnitride or a combination thereof; and may be formed by sputtering.Afterward, a CMP process may be applied to remove excessive copper andplanarize the top surface.

The method 100 proceeds to operation 106 by recessing the underlyingconductive feature 215 such that the top surface of the underlyingconductive feature 215 is below the top surface of the first dielectricmaterial layer 220, resulting in a recess (or recessed trench) 230aligned with the underlying conductive feature 215, as illustrated inFIG. 3. The recessed trench has a vertical dimension D comparable to thethickness T of the recessed underlying conductive feature 215. In someexamples, the ratio D/T ranges from about 10% to about 90%. In someexamples, the ratio D/T ranges from about 20% to about 30%.

In some embodiments, an etching process is applied to etch theunderlying conductive feature 215. The etching process is designed withthe etchant to selectively remove the underlying conductive feature 215while the first dielectric material layer 220 remains intact. Theetching process can be wet etch, dry etch, or a combination thereof. Inthe present embodiment, the underlying conductive feature 215 includescopper; and the etching process includes a plasma etch with an etchantthat includes CH4, H2 or a combination thereof. The plasma etch mayfurther include a carry gas such as argon (Ar) or nitrogen (N2). Invarious examples, the plasma etch uses the gas that includes CH4 and Ar;CH4 and N2; H2 and Ar; or H2 and N2. In a particular embodiment, theplasma etch is a reactive ion etch (RIE).

The recessing process applied the underlying conductive feature 215 atthe operation 106 may be alternatively replaced by or modified to otherproper technique. For example, a self-aligned growth process is appliedto the integrated circuit structure 200 such that a dielectric material(same to or different from that of the first dielectric material layer220) is selectively grown on the first dielectric material layer 220,thereby resulting in the top surface of the underlying conductivefeature 215 is recessed from the top surface of the newly growndielectric material. In other embodiments, the operations 104 and 106may be collectively modified to other procedure to generate such recess.For example, the trench is created by lithography patterning andetching, and thereafter a conductive material is partially filled in thetrench such that recess is automatically generated.

The method 100 proceeds to operation 108 by forming an etch stop layer(ESL) 235 on the IC structure 200, as illustrated in FIG. 4.Particularly, the IC structure 200 has a non-planar top surface sincethe underlying conductive feature 215 is recessed from the firstdielectric material layer 220. The ESL 235 is not planar accordingly.The ESL 235 includes one or more dip portion self-aligned with theunderlying conductive feature 215 and the recess 230. Here,self-alignment between the dip portion and the underlying conductivefeature is understood as an alignment in a top view toward the substrate210. In some embodiments, the ESL 235 is conformal to the top surface ofthe IC structure 200 and the dip portion of the ESL 235 is conformal tothe recess 230. In some embodiments, the dip portion of the etch stoplayer includes a sidewall portion and a bottom portion, the bottomportion being disposed on the underlying conductive feature; the etchstop layer includes a planar portion disposed on the first dielectricmaterial layer; and the bottom portion has a top surface below than abottom surface of the planar portion.

The ESL 235 is designed to provide etch selectivity during subsequentetching and includes a dielectric material different from that of adielectric material layer (240 in FIG. 5, which is to be formed on theESL 235). In various embodiments, the ESL 235 includes a dielectricmaterial selected from silicon nitride, silicon oxynitride, siliconcarbide, silicon carbon nitride or other dielectric material differentfrom that of the dielectric material layer to be formed. For example, ifthe dielectric material layer to be formed includes a low-k dielectricmaterial, such as a porous organic material, the ESL 235 may includesilicon oxide. The ESL 235 is formed by a proper technique, such as CVD.The ESL 235 includes a thickness enough to resist the subsequent etchingprocess. In some other embodiments, the ESL 235 may include a metaloxide, or a metal nitride. For example, the metal oxide may be TiO2,Al2O3, or other metal oxides. For example, the metal nitride may betitanium nitride (TiN), aluminum nitride (AlN), aluminum oxynitride(AlON), tantalum nitride (TaN), or other metal nitrides.

The method 100 proceeds to operation 110 to form a second dielectricmaterial layer 240 on the IC structure 200, as illustrated in FIG. 5.The second dielectric material layer 240 is formed on the ESL 235. Thesecond dielectric material layer 240 fills in the dip of the ESL 235. Insome embodiments, the second dielectric material layer 240 includessilicon oxide, silicon nitride, a low k material, or a combinationthereof. The formation of the second dielectric material layer 240 mayinclude CVD, a spin-on coating or other suitable deposition technology.In some embodiments, the second dielectric material layer 240 is similarto the first dielectric material layer 220 in term of composition anddeposition. After the deposition of the second dielectric material layer240, a CMP process may be applied to planarize the top surface of the ICstructure 200.

In some embodiments, an anti-reflective coating (ARC) film 245 isfurther formed on the second dielectric material layer 240 to reduce thereflection during subsequent lithography patterning or additionallyprovide other functions. In one example, the ARC film 245 includes anitrogen-free ARC (NFARC) material. NFARC material reduces resistpoisoning in sensitive photoresists and may include silicon oxide andmay additionally include carbon, such as carbon-doped silicon oxide.

A mask layer 250 is further formed on the IC structure 200. In someembodiments, the mask layer 250 is a resist layer. In some otherembodiments, the mask layer 250 includes a hard mask material, such assilicon nitride or silicon oxynitride.

The method 100 proceeds to operation 112 to pattern the mask layer 250,thereby forming a patterned mask layer 250 having one (or more) opening255 to define a region (or regions) for metal line (or metal lines), asillustrated in FIG. 6. The metal line refers to a metal line in an uppermetal layer to be formed. In some embodiments, the mask layer 250 is aresist layer, the patterning process in the operation 112 is alithography procedure that includes spin-on coating, exposure anddeveloping. In some embodiments, the mask layer 250 is a hard mask, thepatterning process in the operation 112 includes forming a patternedresist layer on the hard mask 250 using a lithography process; andetching the hard mask through the opening of the patterned resist layerusing the patterned resist layer as an etch mask. After the formation ofthe patterned hard mask, the patterned resist layer may be removed byplasma ashing or wet stripping.

The method 100 proceeds to operation 114 by patterning to define a viafeature (or via features), as illustrated in FIG. 7. In someembodiments, a patterned resist layer 260 is formed on the IC structure200 by a lithography process that includes spin-on coating, exposure anddeveloping. The patterned resist layer 260 includes one (or more)opening 265 that defines a via feature. The via feature defined by theopening 265 and the metal line defined by the opening 255 are overlappedin the top view (as illustrated in FIG. 11) so that the correspondingmetal line is connected with the corresponding via feature. Furthermore,the via feature defined by the opening 265 and the underlying conductivefeature 215 are overlapped in the top view so that the corresponding viafeature is connected with the underlying conductive feature 215.

The method 100 proceeds to operation 116 for via etching, as illustratedin FIG. 7. The second dielectric material layer 240 (and the ARC layer245 is present) is recessed through the opening 265 by a first etchingprocess using the patterned resist layer 260 as an etch mask. The firstetching process is designed and tuned to partially etch the seconddielectric material layer 240 such that the recessed portion is notcompletely through the second dielectric material layer 240. Forexample, the second dielectric material layer 240 is etched to abouthalf of its thickness. In some embodiments, the first etching process iscontrolled by the etching duration. Afterward, the patterned resistlayer 260 is removed by plasma ashing or wet stripping, as illustratedin FIG. 8.

The method 100 proceeds to operation 118 for trench etching, asillustrated in FIG. 9. The second dielectric material layer 240 (and theARC layer 245 is present) is further etched through the opening 255 ofthe hard mask 250 by a second etching process using the hard mask 250 asan etch mask. The second etching process is designed to selectively etchthe second dielectric material layer 240 while the ESL 235 substantiallyremains intact. The second etching process is implemented to partiallyetch the second dielectric material layer 240, such as by controllingthe etching duration. During the second etching process, the seconddielectric material layer 240 within the region defined by the opening255 is only recessed but not completely through the second dielectricmaterial layer 240. However, the second dielectric material layer 240within the region defined by the opening 265 is recessed by the firstetching process and is further etched by the second etching processthrough the second dielectric material layer 240, therefore reaching theESL 235. Accordingly, both the trench 270 for metal and the via (viaopening) 275 for the via feature are collectively formed in the seconddielectric material layer 240. The trench 270 is formed in the upperportion of the second dielectric material layer 240 and the via 275 isformed in the lower portion of the second dielectric material layer 240.

In some embodiments, the second etching process includes dry etch, wetetch or a combination thereof. The second etching process is designedwith an etchant to have etching selectivity such that the second etchingprocess substantially removes the second dielectric material layer 240while keeps the ESL 235 intact. In some embodiments, the etchants usedin the first and second etching process are same. In some embodiments,the second etching process is a dry etch with more etchingdirectionality. In some embodiments, the etchant in the second etchingprocess includes fluorine-containing gas (such as CxFy, which x and yare proper integers), oxygen-containing gas (such as O2), other suitableetching gas or a combination thereof.

After the formation of the trench 270 and the via 275, a third etchingprocess, such as a wet etch, is applied to open the ESL 235. In someembodiments, the ESL 235 includes silicon nitride; and the third etchingprocess includes phosphoric acid. In some embodiments, the ESL 235includes silicon oxide; and the third etching process includeshydrofluoric acid.

The method 100 proceeds to operation 120 to form a metal line 280 in thetrench 270 and a via feature 285 in the via 275, as illustrated in FIG.10. It is noted that the term “via 275” (or “via opening 275”) refers toa void space in the second dielectric material layer and the term “viafeature 285” refers to a conductive feature formed in the correspondingvoid space. In the operation 120, a conductive material is filled in thetrench 270 and the via 275, thereby forming the metal line 280 in thetrench 270 and the via feature 285 in the via 275. The via feature 285and the metal line 280 are collectively referred to as overlyingconductive feature. In various embodiments, the conductive materialincludes copper, aluminum, cobalt or tungsten. In some otherembodiments, the conductive material may include titanium, polysilicon,metal silicide, metal alloy, or combinations thereof. In someembodiments, the overlying conductive feature is similar to theunderlying conductive feature 215 in terms of composition and formation.In the present embodiment, the overlying conductive feature includescopper and has multiple films. In furtherance of the embodiment, theoverlying conductive feature includes a barrier layer lining the trenchand copper filled in the trench. In one example, the overlyingconductive feature is formed by a procedure that includes depositing abarrier layer on sidewalls of the trench; forming a copper seed layer bysputtering; and filling the bulk copper in the trench by plating. Thebarrier layer may include titanium, titanium nitride, tantalum, tantalumnitride, other suitable material, or a combination thereof; and may beformed by sputtering. Afterward, a CMP process may be applied to removeexcessive copper and planarize the top surface. In some embodiments, theARC layer 245 and the hard mask 250 are removed as well by the CMPprocess or another etching process. In some examples, the ARC layer 245and the hard mask 250 are removed by another etching process after theCMP process or before the CMP process.

As mentioned above, the via 275 is defined by the opening 265 of thepatterned resist layer 260 using a lithography process. The opening 265is expected to be aligned with the underlying conductive feature 215.However, the lithography process has intrinsic misalignment. When thespaces between adjacent metal lines get smaller and smaller, and themisalignment tolerances get smaller and smaller, which is a challenge tothe corresponding lithography process. Furthermore, the misalignmentbetween the metal line and the via feature may further introduce qualityand reliability issues. For example, the reliability tests, such as timedependent dielectric breakdown test (TDDB), may have a concern. Thedisclosed method 100 provides a self-aligned process such that themisalignment between the underlying conductive feature 215 and the viafeature 285 is constrained and minimized. Accordingly, the via feature285 is self-aligned with the underlying conductive feature 215. This isexplained below.

As illustrated in FIG. 4, the ESL 235 includes one or more dip alignedwith the underlying conductive feature 215. Particularly, the dip of theESL 235 has a bottom portion and sidewall portions. The bottom portionof the dip of the ESL 235 is substantially lower than the top surface ofthe top surface of the first dielectric material layer 220. This isbecause the underlying conductive feature 215 is recessed and the topsurface of the underlying conductive feature 215 is substantially belowthe top surface of the first dielectric material layer 220. The sidewallportions of the dip are substantially tiled and close to the verticaldirection. In the top view, the sidewall portions are substantiallythicker. When a misalignment occurs, the via 275 is landing on thesidewall portions of the dip in the ESL 235. Considering the etchingselectivity and the vertical thickness of the sidewall portions, thesecond etching process cannot etch through the sidewall portions of thedip in the ESL 235. Accordingly, the via 275 is constrained to bealigned with the underlying conductive feature 215. Furthermore, thedistance between the via feature 285 and the adjacent underlyingconductive feature 215 is labeled as “A” in FIG. 12, which is greaterthan the corresponding distance “a” in an IC structure (illustrated inFIG. 13) otherwise formed, in which the underlying conductive feature215 is not recessed and the ESL 235 has not dip portion. Accordingly,the IC structure 200 in FIG. 12 has a better TDDB than that of FIG. 13.In FIG. 13, the corresponding features are labeled with similar numeralsfor easy comparison but these feature features are different from thosein FIG. 12. For example, in FIG. 13, the underlying conductive feature215 is not recessed and the ESL 235 has not dip portion.

As a comparison, FIG. 14 illustrates the IC structure 200 formed by themethod 100 and FIG. 15 illustrates an IC structure formed otherwise, inwhich the ESL 235 has no dip and the underlying conductive feature 215is not recessed, constructed according to examples. In FIGS. 14 and 15,even the via features 285 are aligned with the associated underlyingconductive feature 215, the IC structure 200 in FIG. 14 still gains someadvantages. Due to that the underlying conductive feature 215 has lesswidth toward the bottom and that the underlying conductive feature 215in FIG. 14 is recessed, the distance “A” between the via feature 285 andthe adjacent underlying conductive feature 215 in FIG. 14 is greaterthan the distance “a” between the via feature 285 and the adjacentunderlying conductive feature 215 in FIG. 15.

As another comparison, FIG. 16 illustrates the IC structure 200 formedby the method 100 and FIG. 17 illustrates an IC structure formedotherwise, in which the ESL 235 has no dip and the underlying conductivefeature 215 is not recessed, constructed according to examples. In FIG.16, even the via 285 is aligned with the associated underlyingconductive feature 215 and the second etching process etches through theESL 235, the IC structure 200 of FIG. 16 still gains some advantages.Due to that the underlying conductive feature 215 has less width towardthe bottom and that the underlying conductive feature 215 in FIG. 16 isrecessed, the distance “A” between the via feature 285 and the adjacentunderlying conductive feature 215 in FIG. 14 is greater than thedistance “a” between the via feature 285 and the adjacent underlyingconductive feature 215 in FIG. 17.

The present disclosure provides an IC structure and a method making thesame. Particularly, the method includes an operation to recess theunderlying conductive feature. The ESL formed on the first dielectricmaterial layer and the underlying conductive feature is not planar andhas a dip portion self-aligned with the underlying conductive feature.By implementing the disclosed method in various embodiments, some ofadvantages described below may present. However, it is understood thatdifferent embodiments disclosed herein offer different advantages andthat no particular advantage is necessarily required in all embodiments.As one example, by recessing the underlying conductive feature in themethod 100, the via feature is constrained to be aligned with theunderlying conductive feature. Furthermore, the distance between the viafeature and the adjacent underlying conductive feature is enlarged,compared with the IC structure otherwise formed, in which the underlyingconductive feature is not recessed and the ESL has not dip portion.Accordingly, the IC structure formed by the disclosed method has abetter TDDB than an IC structure formed otherwise.

Other embodiments and modifications may be implemented without departingfrom the spirit of the present disclosure. In some examples, theunderlying conductive feature 215 includes a metal line and is formed bya single damascene process. In some other examples, the underlyingconductive feature 215 includes a metal line and a via feature, formedby a dual damascene process. In some embodiments, the dual damasceneprocess to form the underlying conductive feature 215 may be similar tothe dual damascene process to form the overlying conductive feature (thevia feature 285 and the metal line 280). In some embodiments, the dualdamascene process to form the underlying conductive feature 215 or theoverlying conductive feature may be a different procedure, such as adual damascene process with a trench-first procedure, in which, trenchfor metal line is patterned first and then the via for via feature ispatterned afterward.

In some other embodiments, the overlying conductive feature includes viafeature formed by a single damascene process. In yet some otherembodiments, the overlying conductive feature includes metal line formedby a single damascene process. In this case, the operations 112 through120 in the method 100 are replaced by a single damascene process. In aparticular example, the single damascene process includes forming apatterned mask 250 as illustrated in FIG. 6. This operation is similarto the operation 112. However, the opening 255 in the patterned mask 250may define a metal line or a via feature. The single damascene processfurther includes performing an etching process through the seconddielectric material layer 240 using the patterned mask layer 250 as anetch mask, as illustrated in FIG. 9. This operation is similar to theoperation 118. However, the etching process in the single damasceneprocess etches from the top surface of the second dielectric materiallayer 240, all way down to the ESL 235, thereby forming a trench for ametal line for a via feature. Afterward, the ESL 235 may be opened by awet etch. The single damascene process then further includes anoperation to form the overlying conductive feature in the trench, asillustrated in FIG. 10. This operation is similar to the operation 120.

In the method 100, a patterning process is used to pattern variousmaterial layers, such as patterning the mask layer 250 or forming apatterned resist layer 260. In various examples, the patterning processis a lithography process that includes exposing a resist layer to aradiation beam. The radiation beam may be a photon beam. For example,the resist layer on a semiconductor wafer may be exposed to anultraviolet (UV) light through a mask having a predefined pattern. Theexposing process may be implemented using a stepper by a step-and-repeatmethod or using a scanner by a step-and-scan method. Other options tothe radiation beam other than photon beams include electron beam and ionbeam. For example, the resist layer may be exposed to an electron beam(e-beam) by an e-beam exposure system (e-beam writer). A pattern may bewritten to the resist layer according to a predefined pattern using thee-beam writer. The exposing process may be further extended to includeother technologies such as a maskless exposing or writing process. Afterthe exposing process, the resist layer may be is further processed by athermal baking process, referred to as a post exposure bake (PEB). ThePEB may induce a cascade of chemical transformations in the exposedportion of the resist layer, which is transformed to have an increasedsolubility of the resist in a developer. Thereafter, the resist layer onthe substrate is developed such that the exposed resist portion isdissolved and washed away during the developing process. The lithographyprocesses described above may only present a subset of processing stepsassociated with a lithography patterning technique. The lithographyprocess may further include other steps such as cleaning and baking in aproper sequence. For example, the developed resist layer may be furtherbaked, referred to as hard baking. The lithography processes implementedin the method may have other variations. For example, an anti-reflectivecoating may be disposed overlying the resist layer, referred to as topARC (TAR). The resist may be negative type so that the PEB process maydecrease the solubility of the exposed resist layer.

Thus, the present disclosure provides a method of fabricating anintegrated circuit in accordance with some embodiments. The methodincludes providing a substrate having a first conductive feature in afirst dielectric material layer; selectively etching the firstconductive feature, thereby forming a recessed trench on the firstconductive feature; forming an etch stop layer on the first dielectricmaterial layer, on the first conductive feature and sidewalls of therecessed trench; forming a second dielectric material layer on the etchstop layer; forming an opening in the second dielectric material layer;and forming a second conductive feature in the opening of the seconddielectric material layer. The second conductive feature is electricallyconnected with the first conductive feature

The present disclosure also provides a method of fabricating anintegrated circuit in accordance with some embodiments. The methodincludes providing a substrate having an underlying conductive featureembedded in a first dielectric material layer; selectively etching theunderlying conductive feature, thereby forming a recessed trench in thefirst dielectric material layer, wherein the recessed trench isvertically aligned with the underlying conductive feature; forming anetch stop layer on the first dielectric material layer, the underlyingconductive feature and sidewalls of the recessed trench; forming asecond dielectric material layer on the etch stop layer; forming a firstpatterned mask on the second dielectric material layer, wherein thefirst patterned mask includes a first opening that defines a firstregion for an overlying conductive feature; forming a second patternedmask on the second dielectric material layer, wherein the secondpatterned mask includes a second opening that defines a second regionfor a via feature; performing a first etching process to the seconddielectric material layer through the second opening of the secondpatterned mask, thereby recessing the second dielectric material layerwithin the second opening; removing the second patterned mask;performing a second etching process to the second dielectric materiallayer through the first opening of the first patterned mask, therebyforming a via opening in a lower portion of the second dielectricmaterial layer and a trench in an upper portion of the second dielectricmaterial layer; and filling in the trench and via opening with aconductive material, thereby forming a via feature in the via openingand an overlying conductive feature in the trench of the seconddielectric material layer, wherein the via feature electrically connectsthe underlying conductive feature and the overlying conductive feature.

The present disclosure provides an integrated circuit structure inaccordance with some embodiments. The integrated circuit structureincludes a first dielectric material layer on a substrate; an underlyingconductive feature disposed in the first dielectric material layer andrecessed from a top surface of the first dielectric material layer; anetch stop layer disposed on the first dielectric material layer and theunderlying conductive feature, wherein the etch stop layer has a dipportion aligned with the underlying conductive feature, and the dipportion is below a top surface of the first dielectric material layer; asecond dielectric material layer disposed on the etch stop layer; and anoverlying conductive feature formed in the second dielectric materiallayer, landing on the underlying conductive feature, and electricallyconnected with the underlying conductive feature.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the detailed description thatfollows. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for forming a multi-layerinterconnection (MLI) structure, the method comprising: forming a firstetch stop layer over a substrate, wherein the first etch stop layer hasa substantially planar top surface; forming a first dielectric layerover the substantially planar top surface of the first etch stop layer;forming a first metal line of the MLI structure in the first dielectriclayer, wherein a top surface of the first metal line is lower than a topsurface of the first dielectric layer, and further wherein the firstmetal line extends through the first etch stop layer and is connected toa conductive feature; forming a second etch stop layer over the topsurface of the first dielectric layer and the top surface of the firstmetal line, such that the second etch stop layer has a non-planar topsurface; forming a second dielectric layer disposed over the firstdielectric layer and the second etch stop layer; and forming a secondmetal line of the MLI structure in the second dielectric layer, whereinthe second metal line is connected to the first metal line.
 2. Themethod of claim 1, further comprising forming a via of the MLI structurein the second dielectric layer, wherein the via connects the secondmetal line to the first metal line.
 3. The method of claim 2, wherein:the second etch stop layer includes a portion that extends between thetop surface of the first metal line and the top surface of the firstdielectric layer; and the via is disposed on the portion of the secondetch stop layer that extends between the top surface of the first metalline and the top surface of the first dielectric layer.
 4. The method ofclaim 2, wherein: the second etch stop layer includes a portion thatextends between the top surface of the first metal line and the topsurface of the first dielectric layer; and the via is not disposed onthe portion of the second etch stop layer that extends between the topsurface of the first metal line and the top surface of the firstdielectric layer.
 5. The method of claim 2, wherein the via extendsthrough the second etch stop layer disposed on the top surface of thefirst metal line and the via has a bottom surface that is lower than thetop surface of the first dielectric layer.
 6. The method of claim 2,wherein the forming the second metal line of the MLI structure and thevia in the second dielectric layer includes: performing a firstlithography process to form a first patterned mask layer over the seconddielectric layer, wherein the first patterned mask layer has a firstopening; performing a second lithography process to form a secondpatterned mask layer over the first patterned mask layer, wherein thesecond patterned mask layer has a second opening that overlaps the firstopening and the second patterned mask layer partially fills the firstopening; etching the second dielectric layer using the second patternedmask layer to form a trench that extends partially through the seconddielectric layer; after removing the second patterned mask layer,etching the second dielectric layer using the first patterned masklayer, such that the trench extends through the second dielectric layerand the second etch stop layer to expose the first metal line; andfilling the trench with a metal material.
 7. The method of claim 6,wherein the trench extending through the second dielectric layer and thesecond etch stop layer includes an upper portion having a first widthand a lower portion having a second width, wherein the first width isgreater than the second width.
 8. The method of claim 1, wherein theforming the first metal line of the MLI structure includes: performing alithography and etching process to form a trench in the first dielectriclayer that exposes the conductive feature; filling the trench with ametal material; planarizing the metal material and the first dielectriclayer, such that a top surface of the metal material is substantiallyplanar with the top surface of the first dielectric layer; and etchingback the metal material, such that the top surface of the metal materialis lower than the top surface of the first dielectric layer.
 9. A methodfor forming a multi-layer interconnection (MLI) structure over asubstrate, the method comprising: forming a first dielectric layer;forming a first metal feature in the first dielectric layer, wherein thefirst metal feature has a first portion and a second portion, whereinthe second portion is disposed over the first portion and a width of thesecond portion is greater than a width of the first portion; forming anetch stop layer on the first dielectric layer; forming a seconddielectric layer on the etch stop layer, such that the etch stop layeris disposed between the first dielectric layer and the second dielectriclayer; and forming a second metal feature in the second dielectriclayer, wherein the second metal feature has a third portion and a fourthportion, wherein the fourth portion is disposed over the third portionand a width of the fourth portion is greater than a width of the thirdportion, and further wherein: the third portion of the second metalfeature physically contacts the second portion of the first metalfeature, and the third portion of the second metal feature includes afirst sidewall and a second sidewall, wherein the first dielectriclayer, the etch stop layer, and the second dielectric layer directlycontact the first sidewall and the etch stop layer and the seconddielectric layer directly contact the second sidewall.
 10. The method ofclaim 9, wherein the forming the first metal feature and the forming thesecond metal feature each include performing a dual damascene process.11. The method of claim 9, wherein the forming the second metal featureincludes: etching a trench in the second dielectric layer that extendsbelow a top surface of the first dielectric layer; lining the trenchwith a metal barrier layer; and filling the trench with a metal bulklayer, wherein the metal bulk layer is disposed over the metal barrierlayer.
 12. The method of claim 9, wherein the forming the first metalfeature includes etching back the first metal feature, such that a topsurface of the first metal feature is lower than the top surface of thefirst dielectric layer and the etch stop layer includes a portion thatextends below the top surface of the first dielectric layer.
 13. Themethod of claim 9, wherein the forming the first metal feature includespartially filling a trench with a metal material, such that a topsurface of the first metal feature is lower than the top surface of thefirst dielectric layer and the etch stop layer includes a portion thatextends below the top surface of the first dielectric layer.
 14. Themethod of claim 9, wherein the forming the first metal feature includesselectively growing a dielectric material over the first dielectriclayer, thereby increasing a thickness of the first dielectric layer,such that a top surface of the first metal feature is lower than the topsurface of the first dielectric layer and the etch stop layer includes aportion that extends below the top surface of the first dielectriclayer.
 15. The method of claim 9, wherein the first metal feature has athickness (T), and a ratio of a distance between a top surface of thefirst metal feature and a top surface of the first dielectric layer tothe thickness is about 20% to about 30%.
 16. A method for forming aninterconnect structure, the method comprising: forming a firstdielectric layer over a substrate; forming a metal line in the firstdielectric layer, wherein a top surface of the metal line is below a topsurface of the first dielectric layer, wherein the metal line isconnected to an integrated circuit device feature; forming an etch stoplayer on the top surface of the first dielectric layer and a portion ofthe top surface of the metal line; forming a second dielectric layerover the top surface of the first dielectric layer, wherein the etchstop layer is disposed between the first dielectric layer and the seconddielectric layer; and forming a metal via in the second dielectriclayer, wherein the metal via extends through the etch stop layer tophysically contact the metal line, wherein the metal via has a firstsidewall and a second sidewall, wherein the second dielectric layer andthe etch stop layer directly contact the first sidewall and the secondsidewall, and further wherein a portion of the first sidewall directlycontacted by the etch stop layer is less than a portion of the secondsidewall directly contacted by the etch stop layer.
 17. The method ofclaim 16, wherein the forming the metal line includes partially fillinga trench in the first dielectric layer with a metal material, such thatthe top surface of the metal line is below the top surface of the firstdielectric layer.
 18. The method of claim 16, wherein the forming themetal line includes selectively growing a dielectric material over thefirst dielectric layer, thereby increasing a thickness of the firstdielectric layer, such that the top surface of the metal line is belowthe top surface of the first dielectric layer.
 19. The method of claim16, wherein the forming the metal via includes: performing a firstlithography process to form a first patterned mask layer over the seconddielectric layer, wherein the first patterned mask layer has a firstopening; performing a second lithography process to form a secondpatterned mask layer over the first patterned mask layer, wherein thesecond patterned mask layer has a second opening that overlaps the firstopening and the second patterned mask layer partially fills the firstopening; etching the second dielectric layer using the second patternedmask layer to form a trench that extends partially through the seconddielectric layer; after removing the second patterned mask layer,etching the second dielectric layer using the first patterned masklayer, such that the trench extends through the second dielectric layerand the etch stop layer to expose the metal line; and filling the trenchwith a metal material.
 20. The method of claim 19, wherein the metalline is a first metal line and the forming the metal via also forms asecond metal line, wherein the metal via connects the first metal lineto the second metal line.